Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__chrono/steady_clock.h

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+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___CHRONO_STEADY_CLOCK_H
+#define _LIBCPP___CHRONO_STEADY_CLOCK_H
+
+#include <__chrono/duration.h>
+#include <__chrono/time_point.h>
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace chrono
+{
+
+#ifndef _LIBCPP_HAS_NO_MONOTONIC_CLOCK
+class _LIBCPP_TYPE_VIS steady_clock
+{
+public:
+    typedef nanoseconds                                   duration;
+    typedef duration::rep                                 rep;
+    typedef duration::period                              period;
+    typedef chrono::time_point<steady_clock, duration>    time_point;
+    static _LIBCPP_CONSTEXPR_SINCE_CXX14 const bool is_steady = true;
+
+    static time_point now() _NOEXCEPT;
+};
+#endif
+
+} // namespace chrono
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___CHRONO_STEADY_CLOCK_H